The present invention relates to a generator stator core, more particularly, to a ventilation duct disposed between magnetic laminations of a generator stator core.
The stator core becomes hot during operation of the electric generator and the heat must be removed to keep it from overheating. Cooling the generator stator core is important for reliable generator performance. In the conventional cooling method, the steel core is cooled by a forced-convection flow of air or hydrogen gas via radial space blocks and cooling channels. In general, hot spots usually appear near the tooth tips of the lamination. Conventionally, the gas smoothly flows inside of the cooling channels to remove heat. These spacer blocks are positioned in such a way to assure tightness of the core during assembly and operation, and not impede or restrict the flow of gas through the stator.
A generator stator core is constructed by stacking layers or xe2x80x9claminationsxe2x80x9d of insulated silicon-iron metal disks together. Inside space blocks or rails are inserted between the layers of the metal disk and these space blocks extend radially from the center of the core. The functions of the inside space blocks are to provide a ventilation passage for a cooling gas and to transfer the weight load due to axial stacking pressure of the laminators. The space blocks are spaced at regular intervals around the circumference of each metal disk. On a conventional stator lamination 1 of arcuate shape, inside space blocks 2 are typically arranged radially and have a cross-section or profile resembling small I-beams. These I-beam shaped space blocks are spot welded to stator lamination, FIGS. 1 and 2. The space blocks are made from one of several thermally conductive materials such as low carbon steel, silicon-manganese bronze, or stainless steel.
Several attempts for enhancing local heat transfer and reducing hot spot temperature in the stator core were made previously. The following patents and applications are hereby incorporated by reference. U.S. Pat. No. 5,869,912 xe2x80x9cDirect-Cooled Dynamoelectric Machine Stator Core with Enhanced Heat Transfer Capabilityxe2x80x9d describes the use of a turbulator element on in ventilation ducts. The spacer blocks have a straight longitudinal profile. Commonly-assigned, co-pending U.S. patent application Ser. No. 09/421,160, filed on Oct. 19, 1999 describes the use of cylindrical compact posts to maximize the flow area for the cooling gas U.S. Pat. No. 4,362,960 xe2x80x9cSpacer Assembly for a Stator Venting Duct of an Electric Power Machine,xe2x80x9d describes slightly curved spacer members having a rectangular profile. While these past attempts alleviate the hot spot problems to some extent, the past space block shapes and the straight radial configurations do not take maximum advantage of heat transfer principles. Since the search is on for improved generator performance, there is a particular need to enhance the heat transfer in a generator stator core.
The present invention pertains to structural arrangements and methods for improving heat transfer in a generator stator core.
According to the present invention, the some embodiments are based on two fundamental heat transfer principles: imparting turbulence to the flow and increasing the convective surface area. One way that enhanced cooling is achieved is in the arrangement of the space blocks. In general, the space blocks, which were conventionally arranged in more or less straight lines, are configured in undulating arrangements, such as a zigzag pattern or a sinusoidal pattern. These configurations force the cooling gas to change direction as it makes its way through the pathway. This disturbance in the flow enhances the cooling of the stator core. Another way to enhance cooling is to change the cross-sectional shape of the space blocks to provide more surface area to promote heat transfer. These two main principles are applied in various permutations to enhance the cooling results of the cooling gas.
In one aspect of the present invention, at least one of the space blocks extends radially extending ventilation pathway includes a longitudinal profile that is defined by an alternating pattern of peaks and valleys. Thus, the cooling gas is influenced to periodically change its direction along the flow path adjacent to the longitudinal profile.
In another aspect of the present invention, a cooling channel extending on a radial axis in a generator stator core for a cooling gas to flow therethrough, comprises axially adjacent stacked lamination in which at least two adjacent space blocks inserted between the stacked laminations. The space blocks extend on the radial axis in the generator stator core. At least one of the space blocks has a plurality of protrusions defining a pattern of peaks and valleys extending from a sidewall of the space block. In this way, the convective contact area of the space block is increased efficient removal of additional heat from the generator stator core.
In yet another aspect of the present invention, a space block for forming radially disposed cooling channels in a generator stator core is provided. Another example is a space block that includes a wavy longitudinal profile for causing local separation and reattachment of the cooling gas boundary layer along the wavy longitudinal profile. Thus, additional heat is removed from the generator stator core.
In another aspect of the present invention, an effective way to enhance convective heat transfer at the stator core space blocks is to use roughened geometries or structures on heated surfaces.
According to another aspect of the present invention, enhanced heat transfer is realized by providing a cooling fluid passage that has a roughness geometry arrangement configured to act as turbulence promoters to increase the rate of heat transfer from the space block to the cooling fluid. In one arrangement the roughness geometry may be formed as a knurled surface.
In yet another aspect of the present invention, a cooling gas ventilation circuit for a generator stator core includes a radial axis extending from a center and comprises at least two laminations and a plurality of adjacent space blocks. The adjacent space blocks are thus disposed between the laminations forming a ventilation duct for a cooling gas to flow through. A heat transfer surface may extend along of the ventilation duct such that at least a portion of a heat transfer surface of the ventilation duct has a knurled pattern. In one arrangement, the heat transfer surface may be formed on a side surface of a space block so as to have a surface profile for enhanced heat transfer. In this way, the thickness of the boundary layer of the cooling fluid adjacent to the sidewalls is reduced and a convective heat transfer coefficient is significantly increased. According to one aspect of the present invention, at least one space block includes knurled sidewalls.
In another aspect, there is provided a space block with thermal passages that extend between adjacent ventilation ducts to increase cooling capacity. In this manner, the cooling gas may exchange between the adjacent cooling channels or ducts so that more uniform heat transfer rate can be achieved over conventional generator stator cores.
In one aspect, a plurality of three-dimensional roughness elements are provided on the lamination surfaces to enhance cooling of the stator core. In one aspect, vortex generators or turbulence promoters are provided on the laminations between the space blocks. As the cooling fluid flow passes over the vortex generators, a several three-dimensional horseshoe vortices are generated in a stagnation area proximate to the vortex generators and the flow separates in the wake of the generators.
The present invention advantageously augments the heat transfer for a generator stator core by increasing the cooling capacity at the stator core. Localized hot spots are greatly reduced by the invention. The generator output rating is increased because the stator temperature is controlled at the lower temperature than conventional cooling systems.
These features and advantages of the present invention will be apparent upon consideration of the following detailed description thereof, presented in connection with the following drawings in, which like reference numerals identifying the elements throughout.